Pressure in fuel tank.

[seeby]

I have read posts on here before about pressure in the fuel tank causing running issues. Ive never had this problem in my Chim. I used to check periodicaly by releasing the filler cap and obviously when refuelling,but never any sign of air build up.My Chim was serviced about a month ago and I had a new pipe from the tank to the pump as the original was perished . Ever since then when the engine is warm ,it wont tick over smoothly (revs from 200/2000 revs and sometimes cuts out) . I now for some reason, find myself checking the filler cap ,in an OCD sort of way,and every time it is really pressurised.Do you think this pressure is affecting the running ?